Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn): New Infrared Nonlinear Optical Materials with Strong Second Harmonic Generation Effects and High Laser-Damage Thresholds

A new family of noncentrosymmetric isostructural compounds, Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn), was successfully synthesized. They crystallize in the tetragonal space group <i>P</i>4̅<i>c</i>2 with <i>Z</i> = 2. Their major structures are composed of infinite cross-connected _<i>∞</i>(HgS₃)_<i>n</i> chains and isolated [MS₄] ligands and show the interesting tunnel features. Interestingly, compared with the structures of A₂Hg₃M₂S₈ (A = alkali metal, Na–Cs), it can be found that the structural symmetries show a gradually rising tendency from Cs to Na analogues as a result of cation size effect, which rarely exists in quaternary alkali metal chalcogenides. Property measurements show that title compounds exhibit strong second harmonic generation (SHG) effects with a phase-matching behavior at 2.09 μm, wide transparency range in the infrared (IR) region, and large laser-damage thresholds (LDTs). Remarkably, Na₂Hg₃Si₂S₈ and Na₂Hg₃Ge₂S₈ achieve the suitable balance between large SHG effects (1.3 and 2.2 × benchmark AgGaS₂) and high LDTs (4.5 and 3 × AgGaS₂), respectively, and can be expected to be potential nonlinear optical (NLO) candidates in the IR region. Moreover, band structures and NLO properties of title compounds are also theoretically studied, and the calculated NLO coefficients are consistent with the experimental observations

Visible-Light-Mediated Construction of Pyrroloindolines via an Amidyl Radical Cyclization/Carbon Radical Addition Cascade: Rapid Synthesis of (±)-Flustramide B

The development of visible-light-mediated synthesis of pyrroloindolines via an amidyl radical cyclization–carbon radical functionalization cascade is reported. The transformation shows a broad substrate scope, tolerating a variety of substitutions on indole aromatic rings and N-centers. Different functionalized alkene systems could be used as radical acceptors. Relying on this strategy, a rapid synthesis of flustramide B was achieved

Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn): New Infrared Nonlinear Optical Materials with Strong Second Harmonic Generation Effects and High Laser-Damage Thresholds

A new family of noncentrosymmetric isostructural compounds, Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn), was successfully synthesized. They crystallize in the tetragonal space group <i>P</i>4̅<i>c</i>2 with <i>Z</i> = 2. Their major structures are composed of infinite cross-connected _<i>∞</i>(HgS₃)_<i>n</i> chains and isolated [MS₄] ligands and show the interesting tunnel features. Interestingly, compared with the structures of A₂Hg₃M₂S₈ (A = alkali metal, Na–Cs), it can be found that the structural symmetries show a gradually rising tendency from Cs to Na analogues as a result of cation size effect, which rarely exists in quaternary alkali metal chalcogenides. Property measurements show that title compounds exhibit strong second harmonic generation (SHG) effects with a phase-matching behavior at 2.09 μm, wide transparency range in the infrared (IR) region, and large laser-damage thresholds (LDTs). Remarkably, Na₂Hg₃Si₂S₈ and Na₂Hg₃Ge₂S₈ achieve the suitable balance between large SHG effects (1.3 and 2.2 × benchmark AgGaS₂) and high LDTs (4.5 and 3 × AgGaS₂), respectively, and can be expected to be potential nonlinear optical (NLO) candidates in the IR region. Moreover, band structures and NLO properties of title compounds are also theoretically studied, and the calculated NLO coefficients are consistent with the experimental observations

Na₄MgM₂Se₆ (M = Si, Ge): The First Noncentrosymmetric Compounds with Special Ethane-like [M₂Se₆]^6– Units Exhibiting Large Laser-Damage Thresholds

Two new noncentrosymmetric compounds, Na₄MgM₂Se₆ (<b>I</b>, M = Si; <b>II</b>, M = Ge), that contain special ethane-like [M₂Se₆]^6– units were reported for the first time. Remarkably, they exhibit high laser-damage thresholds [9 (<b>I</b>) and 7 (<b>II</b>) × benchmark AgGaS₂] and moderate second-harmonic-generation responses with type I phase matching

Synthesis and Characterization of Mid-Infrared Transparency Compounds: Acentric BaHgS₂ and Centric Ba₈Hg₄S₅Se₇

Two mid-IR transparency compounds, namely, acentric BaHgS₂ (BHS) and centric Ba₈Hg₄S₅Se₇ (BHSSe), were successfully synthesized by a conventional solid-state reaction method. The space group of BHS is orthorhombic <i>Pmc</i>2₁ with [HgS₄] tetrahedra and isolated dumbbell-shaped [HgS₂] units, while BHSSe belongs to the orthorhombic space group <i>Pnma</i> with infinite isolated _∞[HgSe₂(S/Se)₂]^4– chains. Raman spectra and thermal analysis of the titled materials were measured. In addition, their band gaps are found to be 1.93 (BHS) and 1.98 eV (BHSSe) from the measured diffuse reflectance spectra. Significantly, the powder BHS sample exhibits a good second harmonic generation (SHG) response of ∼6.5 times compared with that of reference AgGaS₂ at a fundamental wavelength (2.09 μm). The calculated SHG coefficients of BHS are also reported, and the maximum result agrees well with the test observation

Synthesis and Characterization of Mid-Infrared Transparency Compounds: Acentric BaHgS₂ and Centric Ba₈Hg₄S₅Se₇

Two mid-IR transparency compounds, namely, acentric BaHgS₂ (BHS) and centric Ba₈Hg₄S₅Se₇ (BHSSe), were successfully synthesized by a conventional solid-state reaction method. The space group of BHS is orthorhombic <i>Pmc</i>2₁ with [HgS₄] tetrahedra and isolated dumbbell-shaped [HgS₂] units, while BHSSe belongs to the orthorhombic space group <i>Pnma</i> with infinite isolated _∞[HgSe₂(S/Se)₂]^4– chains. Raman spectra and thermal analysis of the titled materials were measured. In addition, their band gaps are found to be 1.93 (BHS) and 1.98 eV (BHSSe) from the measured diffuse reflectance spectra. Significantly, the powder BHS sample exhibits a good second harmonic generation (SHG) response of ∼6.5 times compared with that of reference AgGaS₂ at a fundamental wavelength (2.09 μm). The calculated SHG coefficients of BHS are also reported, and the maximum result agrees well with the test observation

New Compressed Chalcopyrite-like Li₂BaM^IVQ₄ (M^IV = Ge, Sn; Q = S, Se): Promising Infrared Nonlinear Optical Materials

Chalcopyrite-type AgGaQ₂ (Q = S, Se) and ZnGeP₂ are the main commercial infrared nonlinear optical (IR NLO) crystals. Unfortunately, performance defects including low laser damage threshold (LDT), harmful two-photon absorption (TPA), or small birefringence limit their application. With this background, four new compressed chalcopyrite-like IR NLO materials Li₂BaM^IVQ₄ (M^IV = Ge, Sn; Q = S, Se) were successfully synthesized with the typical AgGaQ₂ as templates. Remarkably, Li₂BaGeS₄ and Li₂BaSnS₄ not only maintain the good NLO responses (0.5 and 0.7 × AgGaS₂) but also overcome low LDTs and TPA of commercial chalcopyrites, demonstrating that they satisfy critical demands as promising IR NLO candidates. All of them exhibit phase-matching abilities. Furthermore, the discovery of chalcopyrite-like compounds also provides a feasible design strategy to explore new promising IR NLO materials

Rh(III)-Catalyzed Intermolecular C–H Amination of 1‑Aryl‑1<i>H</i>‑pyrazol-5(4<i>H</i>)‑ones with Alkylamines

An intermolecular C–H amination of 1-aryl-1<i>H</i>-pyrazol-5­(4<i>H</i>)-ones was achieved under mild reaction conditions, using a low catalyst loading and with a broad scope of aminating reagents. This protocol not only provides the first example of rhodium­(III)-catalyzed intermolecular aromatic C–H amination directed by an intrinsic functionality of the substrate/product but also features aminating an existing drug with either primary or secondary <i>N</i>-benzoate alkylamines as the coupling partners

Rh(III)-Catalyzed Intermolecular C–H Amination of 1‑Aryl‑1<i>H</i>‑pyrazol-5(4<i>H</i>)‑ones with Alkylamines

An intermolecular C–H amination of 1-aryl-1<i>H</i>-pyrazol-5­(4<i>H</i>)-ones was achieved under mild reaction conditions, using a low catalyst loading and with a broad scope of aminating reagents. This protocol not only provides the first example of rhodium­(III)-catalyzed intermolecular aromatic C–H amination directed by an intrinsic functionality of the substrate/product but also features aminating an existing drug with either primary or secondary <i>N</i>-benzoate alkylamines as the coupling partners

Na₂ZnGe₂S₆: A New Infrared Nonlinear Optical Material with Good Balance between Large Second-Harmonic Generation Response and High Laser Damage Threshold

The development of frequency-conversion technology in the infrared region is in urgent need of new excellent infrared nonlinear optical (IR NLO) materials. How to achieve a good balance between laser damage threshold (LDT) and NLO coefficient (<i>d</i>_<i>ij</i>) for new IR NLO candidates is still a challenge. The combination of the highly electropositive alkali metal (Na) and Zn with <i>d</i>¹⁰ electronic configuration into crystal structure affords one new IR NLO material, Na₂ZnGe₂S₆. It exhibits excellent properties including a wide transparent region (0.38–22 μm), large band gap (3.25 eV), and especially a balance between a strong NLO coefficient (30-fold that of KDP) and a high LDT (6-fold that of AgGaS₂), indicating a promising application in the IR region. Moreover, novel common-vertex-linked wavelike _∞[GeS₃]_<i>n</i> chains are interestingly discovered in Na₂ZnGe₂S₆, which rarely exist in the reported thiogermanides containing alkali metals. In addition, calculated SHG density and dipole moment demonstrate that the large NLO response is mainly attributed to the cooperative effects of the [GeS₄] and [ZnS₄] units